Electrical machine with two axial fans

ABSTRACT

An electrical machine includes a stator, a rotor magnetically interacting with the stator, a shaft supported on the stator for rotation in a first direction of rotation and in a second direction of rotation which is opposite to the first direction of rotation, wherein the rotor is arranged on the shaft, a first axial fan mounted on the shaft on a side of the rotor for co-rotation with the shaft in the first direction of rotation and having freewheeling capability on the shaft in the second direction of rotation, and a second axial fan mounted on the shaft on the same side of the rotor as the first axial shaft for co-rotation with the shaft in the second direction of rotation and having freewheeling capability on the shaft in the first direction of rotation.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the priority of German Patent Application,Serial No. 10 2011 078 671.6, filed Jul. 5, 2011, pursuant to 35 U.S.C.119(a)-(d), the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to an electrical machine with two axialfans.

The following discussion of related art is provided to assist the readerin understanding the advantages of the invention, and is not to beconstrued as an admission that this related art is prior art to thisinvention.

Electrical machines (especially electric motors and generators)frequently possess a cooling system with a fan and a fan cowl foroptimizing the dissipation of heat. The fan sucks in the cooling air,which is then blown onto the electrical machine via cooling ribs of thehousing. For a good cooling effect a sufficient volume of air or volumeof cooling medium must be conveyed.

The cooling of electrical machines is possible with different fans. Forexample radial fans and axial fans can be used for cooling, which aremounted directly on the motor shaft. Radial fans have fan blades whichextend radially outwards and which are likewise designed to convey thecooling medium radially outwards. The conveyance of the cooling mediumby radial fans is independent of the direction of rotation of theelectrical machine.

With axial fans the fan blades are attached with a specific inclinationto the fan boss. The axial fan conveys the cooling medium in the axialdirection. The direction of conveyance however depends upon thedirection of rotation of the shaft and on the direction of inclinationof the fan blades. Generally the axial fan conveys more cooling mediumthan the radial fan. To utilize the advantages of axial fans(high-volume airflow and low noise) the fans have previously always hadto be tailored to the direction of rotation of the electrical machine.

In addition it is possible to cool an electrical machine with the aid ofan external fan. External fans are generally embodied as axial fans.They have their own drive with a fixed direction of rotation. Thereforethe cooling is undertaken independently of the direction of rotation ofthe shaft of the electrical machine. However external fans alwaysrequire their own drive.

It would therefore be desirable and advantageous to provide an improvedelectrical machine in which independent of the direction of rotation, ahighly effective cooling of the electrical machine is achieved while therequired installation space is reduced as much as possible.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, an electrical machineincludes a stator, a rotor magnetically interacting with the stator, ashaft supported on the stator for rotation in a first direction ofrotation and in a second direction of rotation which is opposite to thefirst direction of rotation, with the rotor being arranged on the shaft,a first axial fan mounted on the shaft on a side of the rotor forco-rotation with the shaft in the first direction of rotation and havingfreewheeling capability on the shaft in the second direction ofrotation, and a second axial fan mounted on the shaft on the side of therotor for co-rotation with the shaft in the second direction of rotationand having freewheeling capability on the shaft in the first directionof rotation.

In an advantageous manner the electrical machine thus possesses twoaxial fans disposed behind one another on the shaft on one side(ventilation side; B-side) of the machine. Thus a flow of cooling mediumis only necessary from the ventilation side independently of thedirection of rotation. The freewheel of the axial fans guarantees inthis case that for each of the directions of rotation only specificallyone of the axial fans will be directly driven. The other axial fanfreewheels and can rotate along with the shaft or in the oppositedirection. The principle of the axial fans guarantees high coolingperformance.

According to another advantageous feature of the present invention, thefirst axial fan can have a boss and a fan wheel connected to the boss,wherein the fan wheel can have a first inclination on a circumference ofthe boss, wherein the second axial fan can have another boss and anotherfan wheel connected to the another boss, wherein the another fan wheelcan have a second inclination on a circumference of the another boss,and wherein in an installed state of the first and second axial fans thefirst and second inclinations are oriented opposite to one another.

In accordance with an embodiment the two axial fans are each supportedwith a roller bearing with return stop on the shaft. This enables it tobe guaranteed in a simple manner that the fans are each only driven in aprespecified direction while there is freewheeling in the otherdirection of rotation.

In accordance with another embodiment the two axial fans are eachsupported with a roller bearing on the shaft and a coupling deviceconnects the first axial fan in the first direction of rotation and thesecond axial fan in the second direction of rotation via a form fit orfriction fit to the shaft. Since the coupling device is separated fromthe roller bearings a high-quality support can be guaranteed.

Specifically the coupling device can have a flywheel which is attachedbetween the two axial fans on a thread of the shaft for rotationalmovement, and which on the sides facing the axial fans has a frictionsurface in each case, with the two axial fans each having acorresponding friction surface in order, depending on the direction ofrotation of the shaft, to establish a friction connection to theflywheel. In particular when the shaft is accelerating the flywheel isthen pushed onto the respective desired axial fan so that a rotationalmovement is imparted to the latter by friction.

The coupling device can also have a latching mechanism with which theflywheel latches releasably resting axially either on the first axialfan or to the second axial fan with a friction connection. Like abayonet connection the flywheel then for example connects to therespective axial fan through the start-up torque and takes said fan withit.

Advantageously the two axial fans are arranged on one ventilation side,with a bearing bracket on which the shaft is supported being disposedbetween the stator and the axial fans, and with a flow of cooling mediumfrom each of the axial fans being able to be conveyed in an axialdirection through the bearing bracket directly to the stator and/orrotor. This has the advantage that, regardless of the direction ofrotation of the electrical machine, the flow of cooling medium conveyedby the axial fans can strike the components to be cooled without beingdiverted.

BRIEF DESCRIPTION OF THE DRAWING

Other features and advantages of the present invention will be morereadily apparent upon reading the following description of currentlypreferred exemplified embodiments of the invention with reference to theaccompanying drawing, in which:

FIG. 1 shows a view of the ventilation side of the inventive motor;

FIG. 2 shows a ball bearing with a freewheel;

FIG. 3 shows an axial fan with a ball bearing including return stop;

FIG. 4 shows a view of the ventilation side of an inventive electricmotor of a second embodiment;

FIG. 5 shows a basic sketch of the coupling device indicated in FIG. 4in a first position;

FIG. 6 shows the coupling device from FIG. 5 in a second position;

FIG. 7 shows an axial fan with rotatable flywheel seen from above;

FIG. 8 shows a basic diagram of ventilation for one direction ofrotation of the motor and

FIG. 9 shows a basic diagram of the motor ventilation for the oppositedirection of rotation.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Throughout all the Figures, same or corresponding elements are generallyindicated by same reference numerals. These depicted embodiments are tobe understood as illustrative of the invention and not as limiting inany way. It should also be understood that the drawings are notnecessarily to scale and that the embodiments are sometimes illustratedby graphic symbols, phantom lines, diagrammatic representations andfragmentary views. In certain instances, details which are not necessaryfor an understanding of the present invention or which render otherdetails difficult to perceive may have been omitted.

Turning now to the drawing, and in particular to FIG. 1, there is shownthe ventilation-side end of a longitudinal section through an electricalmachine (e.g. motor or generator). The electrical machine possesses astator 1 and a rotor 2. The rotor 2 is attached to a shaft 3, which forits part is supported rotatably in a bearing bracket 4, which is part ofa housing of the electrical machine. A stub shaft 3′ of the shaft 3projects on the ventilation side B from the bearing bracket 4. Inaccordance with the invention two axial fans 5, 6 are supported on thestub shaft 3′.

The two axial fans 5 and 6 are each designed for opposing directions ofrotation. In the present example of FIG. 1 the one axial fan 5 isdesigned to run to the left and the axial fan 6 is designed to run tothe right. Only in this respective predetermined run direction does therespective axial fan convey air or cooling medium through to the housingof the electrical machine.

Thus two axial fans 5, 6 acting in opposite directions are provided,with one of the two, depending on the direction of rotation, beingdriven by the electric motor or generator and the second fan being ableto freewheel in this direction. The two fans are connected via acorresponding bearing rotatably to the shaft 3 or the stub shaft 3′.

In a first exemplary embodiment the axial fans 5, 6 are supported inaccordance with FIG. 2 with the aid of a ball bearing 7 with built-inreturn stop. Such ball bearings with return stop are sufficiently wellknown. FIG. 3 shows an axial fan 5, 6, the boss of which features a ballrace 7 with return stop. The ball races 7 are to be oriented accordinglyfor the two axial fans 5, 6, so that a return stop is produced in onedirection for the one fan and a return stop is produced in the otherdirection for the other fan.

In accordance with an alternate embodiment the rotationdirection-dependent, mutual coupling of the fans 5, 6 is undertaken viaa flywheel 8 which is part of coupling mechanism 18 and sits on theshaft 3 (cf. FIG. 4). The flywheel 8 is in shape of a ring and has aninternal thread. It is arranged between the two fans 5 and 6. A section9 of the stub shaft 3 between the two axial fans 5, 6 (cf. FIG. 5) hasan external thread 10 corresponding to the internal thread of theflywheel 8. Through rotational movement the flywheel 8 can move to andfro on the section 10 between the two axial fans 5 and 6, as the basicdiagrams of FIGS. 5 and 6 show.

In the example of FIG. 5 the shaft 3 or 3′ rotates in accordance witharrow 11. Because of the thread 10 the flywheel 8 pushes at least duringthe accelerations corresponding to arrow 12 to the left onto the axialfan 6. The two axial fans 5, 6 are supported with the aid of simpleroller bearings on the stub shaft 3′. As soon as there is now africtional connection between the flywheel 8 and the axial fan 6, theflywheel 8 takes the axial fan 6 with it, so that said fan also startsto rotate in accordance with the rotational movement 11.

If the electrical machine or the shaft 3 is driven in the oppositedirection in accordance with arrow 13 of FIG. 6, the flywheel 8 ispushed by the thread 10 to the right onto the axial fan 5, asillustrated by arrow 14. While axial fan 5 remained free during therotation in accordance with FIG. 5, in the example of FIG. 6, with thereverse rotation it will now be held and carried along by frictionalforce by the flywheel 8. The axial fan 5 now conveys air or coolingmedium to the electrical machine. In this state the other axial fan 6 isable to be freely rotated on the stub shaft 3′.

So that a friction fit is also produced between the flywheel 8 and thecorresponding axial fan 5, 6 when the shaft is rotating at a constantspeed, there can be provision for a latching mechanism 19 for theflywheel 8 to be latched in the respective end position in whichfrictional connection is guaranteed. This can be implemented for exampleby the thread being very flat in the respective end position (especiallyalso infinitely flat). This would thus result in a principle similar tothat of a bayonet connection. When there is a change in the direction ofrotation, the flywheel then rotates as a result of its own inertia fromthe latched position and is then guided across to the opposite axialfan.

FIG. 7 shows an axial fan 5, 6, as can be employed in the presentexemplary embodiment. Located in the boss of the axial fan 5, 6 is asimple roller or ball bearing 15. This makes the axial fans 5, 6basically freely rotatably supported on the shaft 3. In addition afriction ring 16 is attached to the boss of the axial fans 5, 6. If theflywheel is pushed against the friction ring 16, a correspondingfrictional connection is produced and torque can be transmitted via thisfrictional connection. In the example of FIG. 4 the flywheel 8 isagainst the friction ring 16 of the fan 6 for example, so that thelatter is driven by the shaft 3. The other axial fan 5 is freewheelingaccordingly.

FIGS. 8 and 9 show diagrams of the cooling flow situation for differentdirections of rotation of the electrical machine. The diagram of FIG. 8essentially corresponds to that of FIG. 1, with the two axial fans 5, 6merely being depicted schematically. In the example of FIG. 8 the axialfan 6, of which the fan blades have a positive inclination in thediagram, is being driven in the direction of rotation to the left.Consequently a flow or air or cooling medium 17 which is directedtowards the housing or the bearing bracket 4 respectively of theelectrical machine is produced by the axial fan 6 and penetrates thereinto the interior of the housing. The second axial fan 5 is freewheelinghere in the flow of cooling medium flow 17. It can turn along with thedriven axial fan 6 but can also turn in the opposite direction.

If the shaft in accordance with FIG. 9 is rotating in the oppositedirection, then axial fan 5 is driven and axial fan 6 is freewheeling.Since axial fan 5 in the diagram of FIG. 9 has fan blades with anegative inclination, the cooling medium is conveyed here through to thebearing bracket 4 of the electrical machine. The slightly modifiedcooling medium flow 17′ occurs in this case.

In an advantageous manner, for each direction of rotation of the shaftof the electrical machine, only one of the two axial fans which are bothlocated on the ventilation side of the electrical machine, but work inopposite directions, is driven. Regardless of the direction of rotationthere is then always an appropriate flow of cooling medium onto thehousing of the electrical machine. The particular advantage here is thusthat the electrical machine can be cooled from one side without anexternal drive.

While the invention has been illustrated and described in connectionwith currently preferred embodiments shown and described in detail, itis not intended to be limited to the details shown since variousmodifications and structural changes may be made without departing inany way from the spirit of the present invention. The embodiments werechosen and described in order to best explain the principles of theinvention and practical application to thereby enable a person skilledin the art to best utilize the invention and various embodiments withvarious modifications as are suited to the particular use contemplated.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims and includes equivalents of theelements recited therein:
 1. An electrical machine, comprising: astator; a rotor magnetically interacting with the stator; a shaftsupported on a bearing bracket of a housing of the electrical machinefor rotation in a first direction of rotation and in a second directionof rotation which is opposite to the first direction of rotation, withsaid rotor being arranged on the shaft; a first axial fan mounted on theshaft on a side of the rotor for co-rotation with the shaft in the firstdirection of rotation and having freewheeling capability on the shaft inthe second direction of rotation; and a second axial fan mounted on theshaft on said side of the rotor for co-rotation with the shaft in thesecond direction of rotation and having freewheeling capability on theshaft in the first direction of rotation; and a coupling device, whereinthe first and second axial fans are each supported on the shaft with aroller bearing, wherein in the first direction of rotation the clutchdevice form fittingly or friction fittingly connects the first axial fanwith the shaft, and wherein in the second direction of rotation theclutch device form fittingly or friction fittingly connects the secondaxial fan with the shaft, wherein the clutch device has a flywheel whichis rotatably received on a thread of the shaft between the first andsecond axial fans, wherein the flywheel has sides in one to oneconfronting relationship with the first and second axial fans, each ofsaid sides being provided with a friction surface for engaging withrespective corresponding friction surfaces on the first and second axialfans to thereby establish a frictional connection of the first axial fanto the shaft in the first direction of rotation and a frictionalconnection of the second axial fan to the shaft in the second directionof rotation.
 2. The electrical machine of claim 1, wherein the firstaxial fan has a boss and a fan wheel connected to the boss, said fanwheel having a first inclination on a circumference of the boss, whereinthe second axial fan has another boss and another fan wheel connected tothe another boss, said another fan wheel having a second inclination ona circumference of the another boss, and wherein in an installed stateof the first and second axial fans said first and second inclinationsare oriented opposite to one another.
 3. The electrical machine of claim1, wherein the first and second axial fans are each supported on theshaft with a roller bearing with return stop.
 4. The electrical machineof claim 1, wherein the clutch device has a latching mechanism withwhich the flywheel during said frictional connection releasably latchesonto the first axial fan or onto the second axial fan so as to axiallyrest against the first axial fan or the second axial fan.
 5. Theelectrical machine of claim 1, further comprising a bearing bracketinserted between the stator and the first and second axial fans, whereinthe first and second axial fans are disposed on a ventilation side,wherein the shaft is supported on the bearing bracket, and wherein aflow of cooling medium is conveyable by the first and second axial fansin an axial direction through the bearing bracket directly to the statorand/or rotor.